Modification of the Optical Performance of Fiber Bragg Gratings Using Femtosecond Laser Micromachining

This paper describes the use of femtosecond laser pulses to selectively modify the optical performance of as-fabricated fiber Bragg gratings (FBG) written in single mode optical fibers. As a result of the irradiation of FBGs by femtosecond laser pulses generated from a Ti:Sapphire amplifier, the resonance Bragg wavelength is changed, or split into two separate individual wavelengths. In addition, the bandwidth of the reflection peak is increased. Further analyses show that a change of 6.09x10(-4) in the refractive index is achieved in a single pass of the laser beam. Periodic micro-grooves are also inscribed along the fiber using femtosecond pulses. In addition to the optical performance, the sensing performance of the FBGs is increased by inscription of periodic micro-grooves in the cladding of the fiber. The micromachined fibers are used for simultaneous measurement of temperature and concentration of liquids.